An astronaut in a rocket moving with a speed v = 0.6c relative to Earth performs a collision experiment with two small steel balls and concludes that both momentum and energy are conserved in his reference frame. What would an Earth observer conclude?

(a) Momentum and energy are conserved.
(b) Momentum is conserved, but energy is not.
(c) Energy is conserved, but momentum is not.
(d) The collision never takes place because the two balls are never at the same place at the same time.

(e) Neither energy nor momentum is conserved.